The preparation and use of this pyrrolidone derivative is already described in German Offenlegungsschrift 29 02 438 (U.S. Pat. No. 4,178,463), but nothing is said about the yields and purity of the end product. The melting point of 215.degree. C. mentioned in Example 3 of the above-mentioned published German application is an error, which is an indication that the synthesis of this substance pursuant to the process disclosed therein yields the end product with inferior purity (see Comparative Example below).
The pyrrolidone derivative is used for the preparation of 4-amino-hexene-5-acid, (4-vinyl-4-amino-butyric acid) which in turn is useful as an irreversible inhibitor of gamma-aminobutyric acid-transaminase.
The starting compound, 2-vinylcyclopropyl-1,1-dicarboxylic acid dialkyl ester of the formula: ##STR2## wherein R is alkyl of 1 to 5 carbon atoms, preferably methyl or ethyl, may be obtained in accordance with R. W. Kierstead et al, J. Chem. Soc. 1952, pages 3610 to 3616, from a malonic acid ester of the formula EQU H.sub.2 C (COOR).sub.2
and trans-1,4-dibromobutene-2. The substituents R in the starting compound may be identical or different alkyls of 1 to 5 carbon atoms. This compound is always contaminated with 1,1dicarboxylic acid dialkyl ester cyclopentene-3, especially if the 1,4-dibromobutene-2 reactant is a mixture of the cis- and trans-isomers. Moreover, this vinylcyclopropyl compound tends to polymerize.